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Digest: V1 #114
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Purpose: building and operating vacuum tube-based QRP rigs
Subject: glowbugs V1 #114
glowbugs Wednesday, September 17 1997 Volume 01 : Number 114
Date: Tue, 16 Sep 1997 09:07:11 -0700 (MST)
From: Jeff Duntemann <jeffd@coriolis.com>
Subject: Re: 1650Kc IF Can
At 10:29 AM 9/16/97 EDT, km1h @ juno.com wrote:
>Another option is to use a toroid xfmr and miniature Arco style trimmer
>caps. The formulas can be found in various handbooks and QRP manuals.
We talked about this some time back (I don't even want to think how long)
and it came out that toroid cores would make lousy IF transformers. The
reason is that the traditional IF can gets a lot or even most of its
selectivity from the degree of coupling between the two windings, which is
quite loose and adjusted (slightly) by moving a core up and down inside the
form. (The caps adjust the resonant frequency of the windings.)
In a toroid core, the degree of coupling between the two windings is close
to 100%, because virtually all the flux that goes through one winding goes
through the other as well. You won't get nearly as sharp a peak in a
toroid transformer as in a can of traditional design.
Some months ago I happened upon a pi-wound RF choke with an open somewhere.
I pitched it--and regretted it later, because it would have been
interesting to cut the choke (which had four windings) down the middle,
clip the connection between the two windings on the intact half, fish out
the four leads, and see what sort of IF transformer that would make. It
wouldn't be ideal, but it might work, especially since this one had a
hollow core that I might be able to stick a slug into. If anybody runs
across such a choke in the future, consider doing the experiment.
The high road of course would be to clamp your hand drill in a vice, plug
it into an SCR speed control, and chuck up a length of some kind of
RF-friendly tubing. Pull the trigger and press the lock button. Adjust
the speed to something you can cope with, and hand-scramble a winding of
#40 wire into something vaguely resembling a pi. Do it again an inch down
the tubing, then put it on the bench and see what you have. I hope to try
this during the winter, though I have the advantage of a lathe with back
gears.
Now, you RF wizards, how's this for a crazy notion: Get a couple of good
sized toroid cores (T-100 at least) and carefully crack one in half. Loop
the broken one through the middle of the intact one and glue the two halves
back together with super glue or something else with considerable
mechanical integrity. Put one winding on each of the now-interlocked cores.
What would be the degree of coupling between the two windings? I have no
clue, but I suspect it would be pretty loose. Yes?
(I know, there are mechanical problems with a lashup like this, but I'm
curious to know what the magnetic properties would be.)
- --73--
- --Jeff Duntemann KG7JF
Scottsdale, Arizona
Date: Tue, 16 Sep 1997 12:31:00 -0700 (MST)
From: Jeff Duntemann <jeffd@coriolis.com>
Subject: Re: 1650Kc IF Can
At 01:24 PM 9/16/97 -0500, Roberta J. Barmore wrote:
> Your thought-experiment exists; it's an "Austin Ring" transformer, used
>on some AM BC towers to couple the tower-lighting AC across the rather
>high RF potential between tower & ground..
> Never had one apart but they seemed not at all lossy; this would imply
>that chain-linked toroid cores have pretty close coupling. Inter-winding
>capacitance, however, is quite small..
Close coupling is not, however, good in this application. I'm intrigued by
Bob Duckworth's suggestion to stack two toroids with a winding on each and
vary the face-on distance between them somehow to control coupling, which
could easily be varied from slim to none. (As I understand it, the flux
outside the iron powder is pretty thin gruel--just what we want under these
circumstances!)
Anybody ever try this? I guess the question is, Would there be *enough*
coupling to serve as an IF transformer without also acting as a 20 dB
attenuator?
This is an experiment I *must* perform this winter! (I have a length of
threaded nylon rod that is just aching for something to do!)
- --73--
- --Jeff Duntemann KG7JF
Date: Tue, 16 Sep 1997 17:09:51 -0400 (EDT)
From: leeboo@ct.net (Leon Wiltsey)
Subject: tube bargains
Hi Gang
Trying to pick thru a mess of wet soggy tubes. wind blew off a section of roof
at tv shop, has been a hassle. so am offering the following list of tubes
in one batch, to
the first one who gets back to me.. as far as I know most are new still in
soggy boxes
a total of 18 tubes for 46 plus 4 bucks for shipping. Will be offering more
batches as time goes on but this is it for now. let me know by email if u
are interested.
6kn6
6jb6
12ba7
6ag7 2 of these
6sn7
12at7 (2) of these
12bh7
6bq5 2 also
6cg7
6jt6
6kd6
6kv6
6lb6
12jb6
6cg7
THANK THE LORD FOR ALL YOU HAVE
68 yr old semidisabled senior
(stroke got my balance & hand to eye coordination)
ham agn as KF4RCL TECK+ (MUCH HAPPINESS)
BUILD MOST STATION EQUIP
SUB.BA & GB-- NO SOLID STATE
LEON B WILTSEY (Lee) tel. 941 471 3739
4600 Lake Haven BLVD.
Sebring, Fl. 33872 (SEBRING) WHERE THERE IS NO QRM FROM THE LOCALS
Date: Tue, 16 Sep 1997 16:05:24 -0600
From: mack@mails.imed.com (Ray Mack)
Subject: Re[2]: 1650Kc IF Can
<snip>
Close coupling is not, however, good in this application. I'm intrigued by
Bob Duckworth's suggestion to stack two toroids with a winding on each and
vary the face-on distance between them somehow to control coupling, which
could easily be varied from slim to none. (As I understand it, the flux
outside the iron powder is pretty thin gruel--just what we want under these
circumstances!)
Anybody ever try this? I guess the question is, Would there be *enough*
coupling to serve as an IF transformer without also acting as a 20 dB
attenuator?
<snip>
Hey Y'all:
There is a circuit that simulates what you are looking for.
It is called a Cohn filter. This filter is basically what is termed a
coupled resonator filter.
There are 3 topologies that you are probably familiar with.
The first is the crystal ladder filters that you have probably seen
quite a few times in various articles and in the latest ARRL
Handbooks. The next is the bottom coupled filter (uses a small common
inductor) shown in the handbook for at least a decade. The other is
the top coupled filter which uses a capacitor (like in the crystal
filter topology). The purpose of the bottom inductor or top capacitor
is to vary the coupling between the resonators. In an IF can we
pretty much use the common coupling of the core/cores to provide the
coupling magnetically rather than electrically.
See page 12-4 in handbooks 1985 through about 1992.
Ray Mack
WD5IFS
mack@mails.imed.com
Friendswood (Houston), TX
Date: Tue, 16 Sep 1997 17:55:06 -0400
From: "Ornitz, Barry L" <ornitz@eastman.com>
Subject: RE: 1650Kc IF Can
Jeff wrote:
>I'm intrigued by Bob Duckworth's suggestion to stack two toroids with a
>winding on each and vary the face-on distance between them somehow to control
>coupling, which could easily be varied from slim to none. (As I understand
>it, the flux outside the iron powder is pretty thin gruel--just what we want
>under these circumstances!)
>[Ornitz, Barry]
>
In the traditional IF transformer, the coupling between the two tuned
circuits is by mutual inductance. It can just as easily be by
capacitance. In fact, in this situation, capacitance coupling between
the two toroidal windings will provide most of the coupling. A small
coupling capacitance will provide a higher degree of selectivity just as
a small coupling inductance.
Instead of moving the toroids closer or further apart, you might
consider shielding them from each other and adjusting the selectivity
with a "gimmick" capacitor between the high impedance ends of the two
coils.
73, Barry L. Ornitz WA4VZQ ornitz@tricon.net,
> ornitz@eastman.com
>
>
Date: Tue, 16 Sep 1997 16:35:04 -0700
From: Ken Lopez <kjlopez@earthlink.net>
Subject: Re: 1650Kc IF Can
I have about fifty if cans that are new. These were purchased at a
garage sale. How would I determine the operating freq? If any are
1650Kc you would be welcome to them. Is there a way to determine freq
with a dip meter?
Cheers,
Ken, N6TZV
Date: Wed, 17 Sep 1997 10:20:49 +1000
From: Murray Kelly <mkelly@powerup.com.au>
Subject: Re: 1650Kc IF Can
Jeff,
you like to do things the hard way!! :-)
.Get a couple of good
> sized toroid cores (T-100 at least) and carefully crack one in half. Loop
> the broken one through the middle of the intact one and glue the two halves
> back together with super glue or something else with considerable
> mechanical integrity. Put one winding on each of the now-interlocked cores..
******************************************************************
* Murray Kelly vk4aok mkelly@powerup.com.au *
* 29 Molonga Ter. / Graceville/ QLD. 4075/ Australia *
* ph/fax Intl+ 61 7 3379 3307 *
******************************************************************
Date: Tue, 16 Sep 1997 19:57:25 -0500 (CDT)
From: Bob Roehrig <broehrig@admin.aurora.edu>
Subject: Re: 1650Kc IF Can
On Tue, 16 Sep 1997, Jeff Duntemann wrote:
> Close coupling is not, however, good in this application. I'm intrigued by
> Bob Duckworth's suggestion to stack two toroids with a winding on each and
> vary the face-on distance between them somehow to control coupling, which
> could easily be varied from slim to none. (As I understand it, the flux
> outside the iron powder is pretty thin gruel--just what we want under these
> circumstances!)
I agree that the coupling would be pretty small (probably more capacitive
than anything). Maybe the thing to do is keep the 2 toroids apart and
couple by means of a small link winding on each of them.
E-mail broehrig@admin.aurora.edu 73 de Bob, K9EUI
CIS: Data / Telecom Aurora University, Aurora, IL
630-844-4898 Fax 630-844-5530
Date: Tue, 16 Sep 1997 21:40:17 -0700 (PDT)
From: John Kolb <jlkolb@cts.com>
Subject: Re: 1650Kc IF Can
On Tue, 16 Sep 1997, Jeff Duntemann wrote:
> At 10:29 AM 9/16/97 EDT, km1h @ juno.com wrote:
> >Another option is to use a toroid xfmr and miniature Arco style trimmer
>
> and it came out that toroid cores would make lousy IF transformers. The
> reason is that the traditional IF can gets a lot or even most of its
> selectivity from the degree of coupling between the two windings, which is
Rather than have two resonant windings on the same toroid core, sounds
like the thing to do is to use two cores, with a single winding each,
and top couple them with a small cap.
John Kolb KK6IL
Date: Wed, 17 Sep 1997 10:57:34 +0200
From: Jan Axing <janax@li.icl.se>
Subject: Re: 1650Kc IF Can
Jeff Duntemann wrote:
Snipped a little to keep size down...
> In a toroid core, the degree of coupling between the two windings is close
> to 100%, because virtually all the flux that goes through one winding goes
> through the other as well. You won't get nearly as sharp a peak in a
> toroid transformer as in a can of traditional design.
I have another idea. Take two toroids and connect a small capacitor
between the hot ends of them. The capacitance determines the coupling
factor. Perhaps the stray capacitance by placing the two close to
each other is enough? Another way would be to connect the two cold ends
and from here connect a small coil to ground. The inductance of the
little coil determines the coupling. Yes? (or foot in mouth?)
> The high road of course would be to clamp your hand drill in a vice, plug
> it into an SCR speed control, and chuck up a length of some kind of
> RF-friendly tubing. Pull the trigger and press the lock button. Adjust
> the speed to something you can cope with, and hand-scramble a winding of
> #40 wire into something vaguely resembling a pi. Do it again an inch down
> the tubing, then put it on the bench and see what you have. I hope to try
> this during the winter, though I have the advantage of a lathe with back
> gears.
I know a fellow ham nearby who has made an incredibly simple machine that
can wind those nice looking coils found on pi chokes. Not perfect but
very good. If you like, I can have a chat with him about the machine.
> Now, you RF wizards, how's this for a crazy notion: Get a couple of good
> sized toroid cores (T-100 at least) and carefully crack one in half. Loop
> the broken one through the middle of the intact one and glue the two halves
> back together with super glue or something else with considerable
> mechanical integrity. Put one winding on each of the now-interlocked cores.
> What would be the degree of coupling between the two windings? I have no
> clue, but I suspect it would be pretty loose. Yes?
I'll leave this for others but something tells me that you will get almost
no coupling at all. The magnetic lines of the two cores will be perpendicular
everywhere. Maybe some residual coupling due to stray capacitance and
leakage inductance? Interesting idea.
Jan, SM5GNN
Date: Wed, 17 Sep 1997 09:17:39 EDT
From: km1h@juno.com (km1h @ juno.com)
Subject: Re: 1650Kc IF Can
On Tue, 16 Sep 1997 09:07:11 -0700 (MST) Jeff Duntemann
<jeffd@coriolis.com> writes:
>At 10:29 AM 9/16/97 EDT, km1h @ juno.com wrote:
>>Another option is to use a toroid xfmr and miniature Arco style
>trimmer
>>caps. The formulas can be found in various handbooks and QRP manuals.
>
>
>We talked about this some time back (I don't even want to think how
>long)
>and it came out that toroid cores would make lousy IF transformers.
>The
>reason is that the traditional IF can gets a lot or even most of its
>selectivity from the degree of coupling between the two windings,
>which is
>quite loose and adjusted (slightly) by moving a core up and down
>inside the
>form. (The caps adjust the resonant frequency of the windings.)
>
>In a toroid core, the degree of coupling between the two windings is
>close
>to 100%, because virtually all the flux that goes through one winding
>goes
>through the other as well. You won't get nearly as sharp a peak in a
>toroid transformer as in a can of traditional design.
That was not the configuration I had in mind, but in that case you would
be correct.
I was thinking more in the line of :
1. A xtal filter providing the selectivity and the toroid would be
simply the impedance matching device at the input and output. I did
something similar back around 1964 when I added another mechanical filter
in cascade to my 75A4 and used a SS gain equalization stage. Yep; toroids
have been around a long time.
2. Use the toroids in a bandpass filter as the primary selectivty
determining element. I didnt run the filter program on this so not sure
of the insertion losses required for a say 20KHz bandwidth at 1650KHz.
3. Use 2 toroids in a psuedo IF transformer. The coupling and therefore
the selectivity would be determined by the value of the capacitor between
them.
None of the above were meant to supercede the traditional IF can but are
simply alternatives if nothing else is available. It would also be
interesting to measure the Q of a pi-wound coil and a toroid
configuration.
73 Carl KM1H
Date: Wed, 17 Sep 1997 09:27:27 EDT
From: km1h@juno.com (km1h @ juno.com)
Subject: Re: 1650Kc IF Can
On Tue, 16 Sep 1997 21:40:17 -0700 (PDT) John Kolb <jlkolb@cts.com>
writes:
>On Tue, 16 Sep 1997, Jeff Duntemann wrote:
>
>> At 10:29 AM 9/16/97 EDT, km1h @ juno.com wrote:
>> >Another option is to use a toroid xfmr and miniature Arco style
>trimmer
>>
>> and it came out that toroid cores would make lousy IF transformers.
>The
>> reason is that the traditional IF can gets a lot or even most of its
>> selectivity from the degree of coupling between the two windings,
>which is
>
>Rather than have two resonant windings on the same toroid core, sounds
>like the thing to do is to use two cores, with a single winding each,
>and top couple them with a small cap.
>
>John Kolb KK6IL
Absolutely correct John. I replied earlier today to the above but I now
have a number of messages suggesting the capacitive coupling so sorry all
for the duplication.
73 Carl KM1H
Date: Wed, 17 Sep 1997 08:38:39 -0600 (MDT)
From: Art Winterbauer <art@comet.ucar.edu>
Subject: Classic Radio Exchange: 6L6 date?
If I get the chance I'm going to participate in the Classic Radio
Exchange (the 28th I believe). One question and a comment:
* I'll be using a two-step regen receiver (#30 tubes). The article I
built this radio from was reprinting a 1928 article from QST, so I
guess I'll figure 1928 in computing the multiplier. But the
transmitter is just a xtal-controlled 6L6 one-tube transmitter. What
would be a good date to affix to this?
* When using the regen with this 6L6 (a mighty 7 watts out on 80 and
40), the receiver's regen control needs to be re-adjusted after
transmitting. That means the station I'm in QSO with is somewhere
else on the dial and must be re-located. I'd tried shorter antennas,
switching out the antenna, even switching off the plates while
transmitting, all to no avail. About half the time, the regen control
gets upset after being subjected to the mighty signal from the tx
(even when the plates were switched out). So, I've pressed into
service an old Jackson signal generator. It's set to generate a very
weak but audible signal a few Khz above or below the frequency (but
not on the frequency). When readjusting the regen control, I do a
quick search for this signal then move up or down to find the other
guy. Works pretty well!
- --Art WA5OES
Date: Wed, 17 Sep 1997 16:56:34 -0500
From: Conard Murray <cfm5723@tntech.edu>
Subject: Call for GB topics
Hello gals and guys,
I would really like to see some organized activity within the GB community
this winter. How about a topic for each month from October to March?
Something like October is regen receiver month followed by November as
self-excited Hartley month ... these are just examples ..... I want
suggestions from everyone.
During each month those interested will attempt to build and operate an
example of the featured circuit with the help and encouragement of the
entire list. Maybe some interested parties will volunteer to sponsor a
circuit type and offer a prize to the top performer ...?
If this works out like I want it to we will get some great discussion going
on a new topic every month as well as some great operating experiences .....
that's what it's all about, right?
What'cha all think?
73,
ZUT,
de Conard WS4S
End of glowbugs V1 #114
***********************
Created by Steve Modena, AB4EL
Comments and suggestions to modena@SunSITE.unc.edu